Composition for introducing zirconium into magnesium and method of making same



COMPOSITION FOR INTRODUCING ZIRCONIUM INTO MAGNESIUM AND METHOD OF MAKING SAME Edward F. Emley, Clifton Junction, near Manchester, England, assignor to Magnesium Elektron Limited, Clifton Junction, near Manchester, England, a British company No Drawing. Application January 5, 1953, Serial No. 329,744

Claims priority, application Great Britain January 9, 1952 7 Claims. (Cl. 75--93) This invention relates to the production of magnesium base alloys which contain zirconium with or without other alloying constituents but in the absence of elements which combine with zirconium in molten magnesium to form insoluble compounds, alloys of this type being described in British Patent No. 511,137 assigned to the assignee of this application.

It is well-known that considerable difliculties are involved in alloying zirconium with magnesium.

These difliculties can largely be overcome by the method described in the specification of British Patent No. 652,230, also commonly owned by the assignee herein according to which a composition for alloying zirconium with magnesium consists of zirconium chloride and a large percentage of barium chloride and/ or strontium chloride, some zirconium fluoride being also included, if desired, for the purpose of inspissating the chloride remaining after the alloying operation. However, this method also has certain disadvantages, namely (a) the alloying composition is hygroscopic and tends to give rise to porosity in castings made with alloys containing zirconium and zinc, with consequent reduction in tensile properties, and (b) the moisture which is absorbed by the composition decomposes the zirconium chloride and the composition soon becomes no longer satisfactory for introducing zirconium into magnesium. Furthermore, the hydrogen chloride liberated by this decomposition readily corrodes steel, and it has been found impracticable to store these alloying compositions even in airtight steel drums for any protracted period.

With a new to overcoming the difficulty due to hygroscopicity, it has been proposed in the specification of British Patent No. 652,224 to use an alloying composition containing a mixture of fluorides and in the specification of British Patent No. 652,227 it has been proposed to use alkali fluozirconates mixed with chlorides of alkaline earth metals and alkali metals. However, with these processes some diificulty is experienced in regularly obtaining the desirable high mechanical properties in sand castings. A further proposal according to the specification of British Patent No. 652,243 was to use an alloying composition consisting of one or more chlorides of alkaline earth metals including magnesium, together with zirconium fluoride, in the absence of potassium or sodium fluoride. With this process there appears to be no dificulty in readily obtaining high mechanical properties in sand castings provided the composition contains MgClz or CaClz. It has, however, been found that if these chlorides are added in suflicient amount to convert all the ZrFs to ZrCl4 considerable losses of ZrCli due to volatilisation result. If, however, the quantity of magnesium chloride used is sufficient to convert only a part of the zirconium fluoride to zirconium chloride, the excess zirconium fluoride settles out of the molten mixture making it impracticable to manufacture large batches of the composition.

I have now found that it is possible to make a com- 2,788,271 Patented Apr. 9, 1957 potassium chloride, barium chloride and optionally magnesium fluoride in such proportions that the elements in the composition fall within the following percentage ranges, these salts being melted together in an anhydrous condition:

Zr 7-22Vz% (preferably not more than 20% K 10-26 /fi Ba- 6 /z-23% (preferably not more than 20%.) Mg.. 0-6%.

Ol 22V2-42%% (preferably not more than 41%.)

The percentage of chlorine must be between 2 and 6% by weight of the composition greater than that chemically equivalent to metals other than zirconium present in the composition.

The proportions of the above specified salts in the composition fall within the following ranges:

ZrOL; 3 to 10%.

ZrF4 11-29%.

BaClz 1035% (preferably not more than 30%.) MgFz 045%.

It is possible that the final composition may contain a small amount of BaFa formed by slight reaction between the ZrF4 and BaClz.

In a modification of the composition also according to the invention the barium chloride is replaced partly or wholly by one or more of the chlorides of strontium and rare earth metals, the latter being used only when the alloy to be made contains rare earth metals. The replacement by strontium chloride may be effected on the basis of 1% of strontium chloride being equivalent to 0.7% of barium. The replacement by rare earth metal chlorides may be effected on a 1:1 basis. Moreover, the potassi-um chloride may be partly or Wholly replaced by sodium chloride and/ or lithium chloride on a 1:1 basis. The composition may also contain reducible chlorides of one or more of the permissible alloying elements, i. e. Zn, Ag, Tl, Th, Cu, Bi, Pb, Be, Cd, in amounts chemically equivalent to not more than 12% ZrClr, the total of the ZrCli content and the content of reducible chloride expressed in terms of its chemically equivalent ZlCl i content not exceeding 20% and preferably not exceeding 15% by weight of the composition, the relative proportions of the other constituents remaining unchanged. The total chlorine content will still exceed that chemically equivalent to the content of the metals other than zirconium, by between 2 and 6% by weight of the composition, this 2 to 6 percent of chlorine being the chlorine content of the 3 to 10% zirconium chloride.

Some magnesium fluoride which is chemically inert may be included in the composition for the purpose of stiffening the residue remaining after the alloying process.

By the use of this composition it is possible in efiect to obtain the advantages of alloying by means of zirconium chloride, i. e. sand castings With optimum mechemical properties, but since the zirconium content of the composition is largely in the form of zirconium fluoride, the difiiculties heretofore associated with the use of alloying compositions based on zirconium chlorides are avoided. The reason for this is that, during the reaction of the composition according to the present 3 invention with molten magnesium, a cyclic reaction takes place, whereby the zirconium chloride in the composition reacts with the molten magnesium to produce zirconium metal, which alloys with the magnesium, and also magnesium chloride, which then reacts'with a portionfofthe zirconium .fiuoridexto produce a further quantityof .zirconium chloride. This :ZrClr in turn reacts with magnesium with regeneration of MgClz. The processcontinues in cyclic manner until the whole Zirconium content of the composition has been reduced to the metallic form, the reaction always proceeding viazirconium chloride. Since the bulk of the zirconium chloride which ultimately reacts with the magnesium .is formed in situ in a completely anhydrous condition from magnesium chloride which is itself liberated in completely anhydrous condition, porosity'in zirconium containing alloy castings is effectively avoided. In general it is preferred that the composition shall contain zirconium fluoride in excess of the zirconium chloride. The proportion of zirconium chloride is not greater than -%.,and the proportionof zirconium fluoride is preferably greater than The final mixture will have a composition within the following limits: 1

Ou ..016 Zr (which latter corresponds to 12 per c ent Bi... 0 17 ZrCl Whilst the composition may be made by melting the salts together in the above specified proportions this results in a marked tendency for the zirconium fluoride to settle out which renders the preparation of large batches of the composition impracticable. I have, however, now ascertained that the desired composition can be made in a form which is not only effective from the point of view of introducing zirconium into magnesium, but does not exhibit appreciable segregation even when produced in large batches. i

According to this method the zirconium fluoride in the composition is produced in situ in the form of a very fine precipitate by reaction between zirconium chloride and potassium fluoride, insufiicient potassiurnfluoride being however used to-convert all to' the zirconium fluoride in order that the resulting composition may contain 3-10% of zirconium chloride.

Accordingly in order to produce a composition in accordance with the invention the following salts in the proportions stated may be melted togetheri Percent ZrClr 18-50 KF 15-40 KCl 0-35 BaClz 10-35 MgFz 020 the proportion of zirconium chloride exceeding that of potassium fluoride by 320% (preferably 3l8%).

The composition is preferably made by first melting the zirconium chloride with the potassium fluoride and,

if desired, also with the potassium chloride but in the Alternatively, I mayadd .the' potassium fluoride. to a properties on 3 vertical sand cast test bars this melt were as follows:

molten mixture of the zirconium chloride and the potaslumps, and then remeltcd with the'lKF. Melting may be carried out in a crucible with a heavy well fitting lid or if desired in an autoclave. The magnesium fluoride may be added at any desired stage. 7

The composition of the present invention may be used for introducing zirconium into magnesium in severaldifferent ways. For example, the constituent salts of the composition may be melted togetherin a crucible whereupon molten magnesium or' magnesium alloy may be poured into the crucible or solid magnesium or magnesium alloy may be introduced into the crucible and melted therein. Alternatively, the composition may be added in solid onmolten condition to the moltenmagnesium or magnesium alloy. Preferably I add the composition in the form of solid lumps to the magnesiumor .magnesium alloy in a crucible shortly after the charge has begun to melt. In all cases alloying is effected by puddling the melt at a temperature of 7004 00 C., e. g. 800 C. The" following experiment carried out in accordance with the invention is quoted by way ofexample:

Erample I 6 /2 lbs. of aZrCl4 containing melt (50% ZrCl4, 50%

-KCl) and 1% lbs. KF were melted down in a steel crucible fitted with a heavy lid. When this charge melted 1% .lbs. .BaClz were added and stirred in. The mixture was then cast into a shallow tray and the solid melt broken into approximately 2 inch lumps. 1.5 lbs. of these lumps wereadded to la 10 lb. melt of magnesium base alloy con taining 4 /z% zinc. and 0.1% Zr. The melt was puddled for one minute at 800 C. Average tensile properties on three vertical D. T. D. sand cast bars made from this melt The grain size lat the centre of a cast bar was 10.018 mm.

The alloy onan-a'lysis showed a total zirconium content of 0.8% of which 0.7% was in soluble condition: by soluble I mean that part of'the zirconium content which has dissolved in the magnesiumand which is distinguishable from the remainder of the zirconium by being readily soluble (together with the magnesitun which contains it) in an aqueous solution of hydrochloric acid consisting of 30 cc. of HCl (specific gravity 1.16) to :cc. of water, sufficient acid being added during dissolution to mainta in the initial acid concentration.

1% lbs. of the above alloying composition were added to a 10 lb. melt of magnesium base alloy containing'2.8% R..E. (rare earth metal), 2.5% Zn and 0.1% Zr. The melt was puddled for 2 mins. at 800 C. Average tensile poured from 1 inch diameter chill 0.1% P. S., U. T. S Percent El t. s. i. t. s;i on 2 Comparative hygroscopicity. tests were carried out with this melt and with a prefused alloying saltcontaining equal weights of Zl'CLi and KCl. In 40 mins. exposure to air of approximately 80% relative humidity the latter salt picked up 2.5% moisture, but the salt according to the present invention described in this example picked up barely 0.5%.

Example II An alloying substance was prepared with the following chemical composition.

Percent ZI'Ch 3 ZrF4 26 KCl 26 BaClz 27 MgFa 13 This was divided into three portions, two of which were exposed in a humidity chamber maintained at 80% relative humidity. Each portion was used to prepare a Mg-Zn-Zr alloy containing 4%% Zn, and the average tensile results on D. T. D. test bars cast from each melt were as follows:

Tensile properties after Heat Treatment for 16 hrs. at 180 C Time of exposure in humidity chamber 0.1% P. S., U. T. 8., Percent El t. s. i. t. s. i. on 2" I claim:

1. A composition suitable for introducing zirconium into magnesium having the following ingredients:

Percent ZrCh 3 to 10 ZrFl 11 to 29 KCl 0 to 51 NaCl 0 to 51 LiCl 0 to 51 BaCl: 0 to 35 ReCls 0 to 35 SrClz 0 to 50 MgFz 0 to Reducible chlorides of at least one of the metals Zn, Ag, Tl, Th, Cu, Bi, Pb, Be, Cd: from nil to a quantity not exceeding that chemically equivalent to 12 percent of the ZrCli in the composition; the total of the ZrCh and the quantity of other reducible chlorides, if any expressed in ZrClq. equivalency not exceeding 15% by weight of the composition; the composition including at least 19 percent but not more than 51 percent or the chlorides of potsssium, sodium, and lithium in total; the composition also including at least 10 percent but not more than 35 percent of the sum of the barium chloride, rare earth metal chlorides, and seven-tenths of the strontium chloride.

2. A composition as claimed in claim 1 wherein the zirconium chloride content is at least 4 percent and the sum of the barium chloride and seven-tenths of the strontium chloride is less than 30 percent.

3. A composition as claimed in claim 1 wherein the proportion of zirconium chloride is less than that of the zirconium fluoride which exceeds 15 percent.

4. A method of making a composition as claimed in claim 1 wherein the zirconium chloride and the potassium fluoride are first melted together, and then the barium chloride is added to form the zirconium fluoride in situ in the condition of a fine precipitate.

5. A method of producing a composition suitable for introducing zirconium into magnesium wherein the following salts in the proportions stated are melted together:

Percent by weight ZrCl4 18 to 50 KF 15 to 40 KCl 0 to 35 BaClz 10 to 35 MgFz 0 to 20 Percent Zr 7 to 22.5 K 0 to 26.5 Na 0 to 26.5 Li O to 26.5 Ba 0 to 23 Re 0 to 23 Sr 0 to 33 F 5 to 22.5 C1 22.5 to 42.5 Zn 0 to 10 Ag 0 to 19 T1 0 to 21 Th 0 to 16 Cu 0 to 16 Bi 0 to 17 Pb 0 to 19 Be O to 1 Cd 0 to 15 Mg 0 to 6 the percentage of chlorine being between 2 and 6% by weight of the composition greater than that chemically equivalent to the metals other than zirconium present in the composition; the fluorine being present in combination with at least one of the metals and at least partly with the zirconium to form at least 15% ZrFi by weight of the composition; the composition including at least 10 percent but not more than 26.5 percent of potassium sodium and lithium in total; the composition also including at least 6.5 percent but not more than 23 percent of the sum of the barium, rare earth metals, and fivesixths of the strontium; the quantity in total of Zn, Ag, Tl, Th, Cu, Bi, Pb, Be, Cd and Mg not exceeding a total quantity which is chemically equivalent to 5 percent zirconium, all of the elements in the composition being combined in the form of chlorides and fluorides.

References Cited in the file of this patent UNITED STATES PATENTS 2,497,531 Ball et al. Feb. 14, 1950 2,497,537 Emley et a1 Feb. 14, 1950 FOREIGN PATENTS 624,304 Great Britain June 2, 1949 652,222 Great Britain Apr. 18, 1951 652,226 Great Britain Apr. 18, 1951 

1. A COMPOSITION SUITABLE FOR INTRODUCING ZIRCONIUM INTO MAGNESIUM HAVING THE FOLLOWING INGREDIENTS: 